Exodus 19:18-21

18All of Mount Sinai was covered with smoke because the Lord had descended on it in the form of fire. The smoke billowed into the sky like smoke from a brick kiln, and the whole mountain shook violently.

19As the blast of the ram’s horn grew louder and louder, Moses spoke, and God thundered his reply.

20The Lord came down on the top of Mount Sinai and called Moses to the top of the mountain. So Moses climbed the mountain.

21Then the Lord told Moses, “Go back down and warn the people not to break through the boundaries to see the Lord, or they will die.